You haven't said anything that I don't already know, and you haven't countered what I have pointed out. The fact remains that your proposed design--to put the diaphragm directly behind the front element--is incorrect and reflects an ignorance of camera lens design principles.

Oh, and by the way, when you can show me an unaided normal human eye that has the resolving capability of a 500mm lens, then you might have the faintest semblance of a reasonable comparison.

wickerprints wrote in post #8603704You haven't said anything that I don't already know, and you haven't countered what I have pointed out. The fact remains that your proposed design--to put the diaphragm directly behind the front element--is incorrect and reflects an ignorance of camera lens design principles.

How have I not countered what I pointed out? Either you haven't read the reply, or failed to understand the optics behind it.

These were your points:

1. Cornea/aqueous humour/vitreous humour have refractive properties.

Fixed focal length with fixed plane of focus. A window also has refractive properties. Easily replaced with 1 piece of glass. You can put that piece of glass anywhere, depending on its shape.

2. The lens of the eye is capable of flexing to focus.

A camera lens does the same thing by moving multiple rigid elements, essentially creating a multipartite lens that 'flexes' by moving each element individually. There's no optical law saying these elements have to be big.

3. The leaves of a camera's aperture diaphragm are rigid.

And they can also rotate out of the way. By design, a wide-open diaphragm doesn't take up any more space than a fully closed one. This is part of the wide end of the cone.

4. You need a long barrel so that the elements can move.

This is the same whether you're using large elements or small elements. Smaller, more strongly curved elements generally don't need to move as far. Even if they did, you're still saving on diameter, even if not in length.

5. There is a certain minimum width, since internal motion is achieved through a series of nested cylinders.

These nested cylinders clearly do not need to be very wide, as there are many perfectly good lenses with small diameters. In other words, it is not the limiting factor for barrel width in longer lenses - the limiting factor is minimum aperture diameter to achieve a certain f-stop.

wickerprints wrote in post #8603704Oh, and by the way, when you can show me an unaided normal human eye that has the resolving capability of a 500mm lens, then you might have the faintest semblance of a reasonable comparison.

1. Not a fair comparison. The human eye produces an image on the retina, which is smaller than a crop sensor. Obviously a larger sensor will require a larger image circle, which requires a larger lens. I am not advocating a 500mm lens the size of a human eyeball.

2. Not a fair comparison. A larger sensor will usually have greater resolving power than a smaller one. The retina is smaller than a crop sensor. The fovea (the part that's actually sharp) is many times smaller. This is a sensor limitation, not a lens limitation.

3. Not a fair comparison. The neurons supplying the retina enter the eye at the optic disc, or 'blind spot'. They then travel in front of the retina to their position, entering the retina from the front. Naturally this somewhat diffracts the light and reduces resolution. Just like placing a very strong anti-aliasing filter in front of a camera sensor. Some animals do not have this problem.

4. Not a fair comparison. The human eye is not a precision-made machine. There are remnants of the developmental hyaloid artery within the aqueous humour. Corneas are rarely perfect. Every copy is different. Just like Sigma lenses. If one came up with an ideal design and replicated it every time, you could have an extremely high-resolution system. It's all about shape and precision, not size. You can do that with camera lenses. With human eyes, you're stuck with what you have.

Admittedly EF lenses have AF mechanisms to incorporate and that adds bulk. But fast lenses do not have to be as bulky as they are! Compare Tamron f/2.8 AF lenses with Canon f/2.8 AF lenses to convince yourself.

Wilt wrote in post #8604751Q: "Can lenses be made smaller?"A: "Yes, simply look at Olympus OM lenses compared to Canon EF lenses for a real Mutt and Jeff comparison!"

Admittedly EF lenses have AF mechanisms to incorporate and that adds bulk. But fast lenses do not have to be as bulky as they are! Compare Tamron f/2.8 AF lenses with Canon f/2.8 AF lenses to convince yourself.

I wish Canon would make a 24-70 or 24-105 equivalent (in FF 35mm) zoom lens for 1.6x crop that has a small, constant aperture throughout the focal range. It would be something like "EF-S 15-45mm f/2.8 [IS] USM" or "EF-S 15-65mm f/4.0 [IS] USM" (IS being a a nice addition, but not absolutely necessary).

I know about the new, upcoming EF-S 15-85mm f/3.5-5.6 IS USM; it has an ideal focal length range, but the variable aperture makes it less tentalizing for me (I have no doubt it will be welcome by many --> see KenjiS :cool. Even if it was just a constant f/4.0 (I'd prefer 2.8, of course), I would be willing to lose one stop on the wide end to gain three stops on the tele end.

As for the build, somewhere along the 17-55's build is fine with me, although I would certainly appreciate L quality build. Still, the optics are way more important than the build, at least in my case (I take good care of my stuff and don't try too many "stunts" like shooting directly under heavy rain without a cover).

But let me make it clear that by no means do I want or expect L quality on a EF-S lens for cheap. I happily spent ~$1,000 for my 17-55, and I'm willing to dish out in the range of $1,200 - $1,500 for one of the two wished-for lenses I detailed above if they have L, or close to L, quality optics and build, and perhaps IS as well.

Obviously, in the long run I intend to go FF (5D MkIII, maybe?) and both the 24-70L and 25-105L are lenses I want in my kit (I will also consider any updates to those if it happens in the timeframe when I am ready to buy). But at the moment I feel a little limited with the choices of quality lenses offered by Canon for 1.6x crop. Maybe I should look into Sigma or Tamron. I have also considered the 17-40 f/4L, which comes close to the 15-45 range I mentioned aboved.

In the meantime, my two mainstay lenses are the EF-S 17-55mm f/2.8 IS USM and EF 70-200mm f/2.8L IS USM, so I have a coverage gap between 55mm and 70mm. I have the EF 28-105mm f/3.5-4.5 II USM, but I stopped using it after getting the 17-55; the quality just isn't there for me with that lens. I use a very simple solution to deal with the coverage gap, and it's inexpensive: walk up closer to the subject/scene when using the 17-55, or step further back from the subject/scene when using the 70-200.

krepta wrote in post #8614126As for the build, somewhere along the 17-55's build is fine with me, although I would certainly appreciate L quality build. Still, the optics are way more important than the build, at least in my case (I take good care of my stuff and don't try too many "stunts" like shooting directly under heavy rain without a cover).

Actually i did that with my 17-55 once...it didnt hurt it..

oddly enough, for a lens renowned for sucking dust its pretty waterproof o_O

Old Thread.... But I fully agree. I owned the 17-55 IS lens. I hated it every second I had it and traded it for a 24-70L as soon as I could. That lens simply was over priced. Though Canon has gotten a little better since the last post in this thread they're not that much better. The 18-200 fascinates me but then again so does the 28-300L and neither would I own.

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